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(11) | EP 0 246 558 B1 |
| (12) | EUROPEAN PATENT SPECIFICATION |
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| (54) |
High-tenacity, high-flexibility polymeric blend Hochfestigkeit und Hochbiegsamkeit erzeugende Polymerzusammensetzung Mélange de polymère à haute ténacité et à haute flexibilité |
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| Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). |
[0001] EP-A-195 829 (to be considered under article 54(3) EPC) discloses a polymer blend composition comprising
(a) at least 20 % by weight of an olefin polymer;
(b) at least 5 % by weight of a monovinylidene aromatic polymer, and
(c) a compatibilizing amount of a monovinylidene aromatic polymer-grafted alpha-olefin copolymer.
[0002] The patent abstracts of Japan, 1982, vol.6, No. 231 are directed to the improvement of the impact resistance of a poly-alpha-olefin by the addition of a copolymer (b) prepared by a graft polymerization of an ethylene-alpha-olefin-polyene ternary copolymer with a polymerizable unsaturated monomer containing at least 25% by weight of an alkenyl aromatic monomer (styrene), wherein the weight ratio ethylene-alphaolefin-polyene copolymer/polymerizable unsaturated monomer is 1/3 to 20/1. The amount of the copolymer (b) is from 1 to 100 parts by weight to 100 by weight of the polyolefin which corresponds to a range from 99 to 50 % by weight of the polyolefin with respect to the blend copolymer (b) + polyolefin.
[0003] The object of the present invention is a thermoplastic polymeric blend endowed with high tenacity and high flexibility characteristics.
[0004] More particularly, the present invention relates to a thermoplastic blend endowed with high tenacity and high flexibility, particularly suitable for the injection moulding and thermoforming of compact or foamed pieces for uses in the packing, household electrical appliances, motor cars, telectronic, etc., fields.
[0005] The polymeric blend of the present invention comprises a styrene polymer or copolymer reinforced with ethylenepropylene-diene rubber (EPDM) and polyethylene, characterized in that the amount of polyethylene is higher than 15 % and up to 38 % by weight with respect to the blend, the amount of the ethylene-propylene-diene (EPDM) in the mixture is from 5 to 50 % by weight and when the polyethylene/EPDM weight ratio is higher than 1,5, the weight ratio of the rigid phase to the EPDM rubber, in the polymeric blend, does not exceed 3.5.
[0006] The term "polyethylene" comprises an ethylene polymer having a density of from 0.90 to 0.97, such as, for example, the polymers known as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE) and high-density polyethylene (HDPE).
[0007] The term "styrene polymer or copolymer reinforced with ethylene-propylene-diene (EPDM) rubber", comprises a polymeric material consisting of:
a) a rigid matrix constituted by polystyrene, or by a styrene copolymer containing up to 40% by weight of an acrylic monomer, and
b) an elastomeric phase dispersed in the rigid matrix and constituted by EPDM rubber either totally or partly grafted with chains of polystyrene or of styrene-acrylic monomer copolymer of the rigid matrix.
[0008] The term "acrylic monomer", comprises above all, and preferably, acrylonitrile; however, other ethylenically-unsaturated acrylic monomers, such as methacrylonitrile, can be used with similar advantages.
[0009] The styrene polymer or copolymer reinforced with EPDM rubber can be used as such, or blended with polystyrene, or with a styrene copolymer, such as styrene-acrylonitrile (SAN) copolymer, in an amount of up to 50% by weight.
[0010] The styrene polymer or copolymer reinforced with EPDM rubber can be obtained by either dissolving or dispersing the EPDM rubber into the styrenic monomer or monomers mixture, optionally in the presence of a solvent, and polymerizing the resulting dispersion by mass, suspension or continuous-mass polymerization as disclosed, e.g., in IT-B-792,279 and in GB-B-2,059,427.
[0011] In the polymeric blend of the present invention, the polyethylene may range from an amount higher than 15% by weight up to 38% by weight and correspondingly the styrene polymer or copolymer reinforced with EPDM rubber may range from 62% up to an amount lower than 85% by weight. However when the polyethylene/EPDM weight ratio is higher than 1.5, the weight ratio of the rigid phase to the EPDM rubber, or elastomeric phase, in the polymeric blend, does not exceed 3.5.
[0012] The preparation of the polymeric blend according to the invention can be carried out by blending the starting polymeric products, in pellet form, in a mill; the blend is then processed in the plastic state, at high temperature, in a screw extruder-pelletizer.
[0013] The polymeric blends of the invention are endowed with good mechanical properties, have a high homogeneousness degree, are not subjected to delamination and are suitable for injection-moulding and thermoforming according to conventional methods.
[0014] The polymeric blends of the present invention may also contain different agents, such as, e.g., stabilizers, flame retarding agents, antistatic agents, and so forth, for the manufacturing of particular articles endowed with UV-resistance, self-extinguishing properties, low surface attraction for dusts, etc.
[0016] As such foaming agents, there can be used:
a) the chemical foaming agents, such as, e.g., azodicarbonamide, which are added to the polymeric blend and are decomposed inside the apparatus (either injection-press or extruder) for obtaining lighter objects or semifinished articles having a density up to three times lower than of the starting product;
b) the physical foaming agents, such as, e.g., the short-chain aliphatic hydrocarbons (propane, butane, pentane, etc.), or halocarbons, such as freon, by which the pellets of the polymeric blend are impregnated and then foamed and sintered, to the purpose of obtaining articles having density values up to 30 times lower than of the starting product.
Examples 1-4 (Examples 3 and 4 being comparative examples)
[0017] The components of the blend as reported in the following table are blended on a rotary-arms mill, at 100 rpm, and the resulting blend is extruded on a twin-screw WERNER & PFLEIDERER ZSK53 extruder, at a temperature of the molten polymer of 240°C.
a) a rigid matrix constituted by polystyrene, or by a styrene copolymer containing up to 40% by weight of an acrylic monomer, and:
b) an elastomeric phase dispersed in the rigid matrix and constituted by EPDM rubber either totally or partly grafted with chains of polystyrene or of styrene-acrylic monomer copolymer of the rigid matrix.
Polymermischung 3,5 nicht überschreitet.
a) einer starren Matrix, gebildet aus Polystyrol oder aus einem Styrolcopolymeren, enthaltend bis zu 40 Gew.-% eines Acrylmonomeren, und
b) einer elastomeren Phase, die in der starren Matrix dispergiert ist und aus EPDM-Kautschuk gebildet wird, der entweder vollständig oder teilweise mit Ketten von Polystyrol oder von Styrol-Acrylmonomer-Copolymer der starren Matrix gepfropft ist.
(a) une matrice rigide constituée par du polystyrène, ou par un copolymère de styrène comprenant jusqu'à 40% en poids d'un monomère acrylique, et
(b) une phase élastomère dispersée dans la matrice rigide et constituée par un caoutchouc EPDM soit totalement soit partiellement greffé avec des chaînes de polystyrène ou d'un copolymère styrènemonomère acrylique de la matrice rigide.